A Question about Worldbuilding/Astronomy

[Metra]

Hi All, I've done a ton of searching on the internet looking for some reliable information on realistic/scientific Worldbuilding resources and there is a good deal out there, yet i've hit a block that I can't get past.

My homebrew world has a moon, which itself has water, and atmosphere and life on it. I'm looking for some information on how this satellite (proportionally the same size as our own moon) would act, obviously the terrestrial tides would be similiar, but what about the moon's tides?

One could assume that the tides would be treacherous to say the least, yet my assumption is that the sun being in a different position of guiding the tides would help smooth the effects of the planet on the moon.

Any help will be appreciated, any websites or your own thoughts would be greatly appreciated, thanks.

 

[Grymar]

Using real world physics? That's a hard one to work out.

The moon's gravity isn't strong enough to keep an atmosphere in place, and thus water will evaporate into space immediately. Mars, at about 2/3rds the size of Earth, is able to keep an atmosphere and probably at one time (and maybe even periodically today) had running water.

Titan would probably be a good analogy...it has about twice the mass of our moon and is able to hold on to an atmosphere.

Tides would be significantly stronger than what you would see here on Earth. And yes, the sun's position would make a difference, but there are a lot of questions you'd have to get into such as the orbital period of the moon and its rotational period, plus the primary planet's distance from its star.

We do have two tides, a lunar tide and a solar tide, although the solar tide is weak enough that it is often ignored, so there would be an effect.

HAVING SAID ALL OF THAT, think of a cool effect and do it. If your players break out orbital physics, then its time to beat them with the DM hammer.

 

[Metra]

I never thought of titan

After you mentioned Titan I went and researched this planet sized moon and found that if I made the primary larger, and the size of the satelitte increased proportionally (large enough to hold an atmosphere) you have a realistic scenario for water.

The Tides will likely be massive, and the Solar tide is only 1/3 the pull of the primary, making a Lunar eclipse having incredibly high tides on two sides of the planet. I don't think this will be a major concern seeing as the moon is designed to be mainly comprised of shallow oceans with only minor landmasses, which considering that most the land may very well dissapear daily makes for an interesting world.

Regardless thanks for the heads up on Titan.

 

[PapersAndPaychecks]

Is it moon-like to the extent of being phaselocked with only one face to the primary?

 

[Psion]

Using real world physics? That's a hard one to work out.

The moon's gravity isn't strong enough to keep an atmosphere in place, and thus water will evaporate into space immediately. Mars, at about 2/3rds the size of Earth, is able to keep an atmosphere and probably at one time (and maybe even periodically today) had running water.

Titan would probably be a good analogy...it has about twice the mass of our moon and is able to hold on to an atmosphere.

Actually, it's not. Titan is smaller than both Mars and Ganymede, which have thin or no atmosphere, respectively.

Scientists believe that titan is continually replenishing its atmosphere and is largely formed of ices that, in an anolog to volcanism on earth, liquify and erupt.

 

[Psion]

Anyways, to the OP...

There was a pretty decent article on habitable moons on Freelance Traveller. Not 100% up to date scientifically, but will probably get you headed in the right direction:
http://www.freelancetraveller.com/features/science/gasgiants.html
(Scroll down to "surface habitable moons")

You'll note that this only talks about moons of gas giants. It would take a gas giant (or similarly large world) to have a moon large enough to retain an Earth like atmosphere, unless it's artificial.

 

[PapersAndPaychecks]

You could have two planets of any arbitrary size orbiting a common centre of gravity. Psion's right for a given definition of "moon", but I don't see that this is any more than semantics.

 

[Metra]

Intent

The System in question is that of a Primary, about 1.8 times the size of the Earth and one satellite which is proportianally the mass and size of the moon given the above size/mass.

The mass of Titan is only .0225 that of earth, and at that mass it retains an atmosphere, so I made the moon that mass and it should work, right?

Although I thought of having a two planet system, it's not the intent and would not be habitable in the traditional sense. Climate and weather systems would be unstable do to the fact that there would be little receding tide as they would pull water in the same direction and rolling across the planet creating supwaves that would wipe over the continents daily, right?

Psion thanks for the article, I'll check it out.

 

[Psion]

You could have two planets of any arbitrary size orbiting a common centre of gravity. Psion's right for a given definition of "moon", but I don't see that this is any more than semantics.

IIRC, such a dual planet system wouldn't be stable in an appropriate orbit from an appropriate sized star.

 

[Psion]

The System in question is that of a Primary, about 1.8 times the size of the Earth and one satellite which is proportianally the mass and size of the moon given the above size/mass.

The mass of Titan is only .0225 that of earth, and at that mass it retains an atmosphere, so I made the moon that mass and it should work, right?

See my post about titan above. It'd be a Mars or Ganymede-like moon.